In recent years, there continues to be dramatic density increases in integrated circuit technology for semiconductor chips. For example, the minimum feature size of lithography, such as the size of MOSFETs, has been reduced to one micrometer and below. In the fabrication of precision capacitors in conjunction with FET devices on the same chip at these reduced dimensions, it is increasingly difficult to maintain manufacturing parameters such that precise outputs from these devices are still available.
Many applications implemented on modern semiconductor chips require accurate voltages. A classic example is writeable memory, which requires the amplitude of the erase voltage to balance the write voltage of the writeable memory cells. If the erase voltage does not accurately match the write voltage, the memory cell will typically continue to store a binary “1” value, rather than the intended “0” binary value. To insure that the write voltage and erase voltage are generated properly, an on-chip voltage regulation circuit (e.g., a voltage regulator) is typically required.
Unfortunately, there are several on-chip and environmental effects that consistently counteract the regulation of on-chip voltages. Examples of these include temperature effects and manufacturing process variations. Relatively extreme variations in temperature, for example, the operating temperature of active devices within a voltage regulator, often affect the resistance, capacitance, voltage and current flow of on-chip components, and thus the overall semiconductor chip itself. In addition, process variations typically affect line spacings and the thickness of oxides, metals, and other layers of the semiconductor wafer, which consequently can affect on-chip voltages. This disclosure is directed to combating the problems caused by temperature fluctuations and process variations in voltage regulator circuitry.